1. Field of the Invention
The invention relates to a sensor for measuring pressure and/or force, comprising at least one measuring assembly having at least one piezoelectric measuring element subjected to compressive stress for dynamic pressure and/or force measurement, and a diaphragm for introducing the pressure and/or the force onto at least the piezoelectric measuring element.
2. The Prior Art
Piezoelectric pressure sensors utilize the effect that the surfaces of piezoelectric materials become electrically charged proportionally to a mechanical stress that is applied, so that subsequently a processable charge signal can be generated therefrom. Such sensors are active sensors which are well suited for dynamic measuring technology, In addition, piezoresistive pressure sensors are known which change the electrical resistance thereof under mechanical stress.
A sensor is described in US 2006137456 A, which comprises a gallium nitrite diaphragm seated on a substrate, which is etched to form a cavity. This diaphragm exhibits both a capacitive response and a plaza response to external stimuli. The sensor further comprises a circuit for measuring at least one of these responses and can be used to measure external stimuli, such as pressure, force or mechanical vibrations.
So as to allow both dynamic and static pressure measurements using only one sensor, it has been proposed in JP 2004226294 A to form electrodes on two surfaces on a substrate comprising piezoelectric material. A diaphragm comprising insulating material and a third electrode is provided on one side, and a dummy electrode is provided on the other side, wherein the substrate is bonded to the diaphragm so that the second and third electrodes are located opposite each other. In this way, the static pressure can be determined based on the capacitance between the second and third electrodes, and the dynamic pressure can be determined based on the piezoelectric effect of the substrate.
It was the object of the present invention to provide a further embodiment of a sensor for pressure or force measurement as indicated above which allows improved detection of static and dynamic effects.
So as to achieve this object, the sensor according to the invention is characterized in that a further measuring assembly based on a different physical measuring principle is provided for static pressure or force measurement. As a result, a self-test function of the sensor is possible with high precision and reliability, in addition to the simultaneous in-phase measurement of dynamic and static pressures or forces, when the dynamics drop into the range of the measuring principle for static measurements. By combining static and dynamic measurements, an in-phase signal having higher bandwidth is obtained.
A first embodiment variant of such a sensor is characterized in that at least one region of the sensor which is influenced by the pressure and/or the force is provided with a strain measuring structure for the static pressure and/or force measurement.
To this end, the strain measuring structure may be provided on a surface of at least one measuring element to which the pressure or the force is applied, wherein the measuring element is preferably operated in transversal mode.
As a further variant according to the invention for combining dynamic with static pressure and/or force measurement, the above-described sensor can also be characterized in that at least one piezoelectric element for the static pressure and/or force measurement is operated as a piezoelectric resonator subjected to compressive stress by the diaphragm.
If, according to a further embodiment, a strain measuring structure is provided in an orientation deviating from the direction of the compression, preferably normal relative to this direction, the temperature-related dimensional change can be determined from the relationship of the signals of all the strain measuring structures, and thus a temperature compensation can be carried out.
However, a temperature compensation can also be carried out according to a different embodiment of the sensor if at least one further strain measuring structure is provided in a region of the sensor not influenced by the pressure and/or the force.